Seeing the edges of the Universe: 5 years of WMAP data

This week saw the release of five years of measurements and results from the …

This week, NASA revealed five years' worth of collected data from the Wilkinson Microwave Anisotropy Probe (WMAP). The WMAP probe looked at what used to be the light emitted during the early years of the universe. However, over the intervening 13.7 billion years, the expansion of the universe stretched the light out so that it is now detected as microwaves. By collecting and analyzing these microwaves, the WMAP probe has helped answer questions about the age of the universe, what it is made of, and how it developed.

Five-year WMAP full sky map

A great deal of what we learned from the WMAP study has come from the full sky maps, which show the temperature distribution in the universe. The average temperature is 4.905 oR, and fluctuates by a few microdegrees. However, these minor fluctuations can tell us a great deal about the evolution of the universe itself. The patterns formed in these fluctuations are a result of sound waves in the early universe, and previous works had found the first and second harmonics of this sound. The latest WMAP data, has clearly discovered the third harmonic. This new discovery has lead to further experimental evidence that a "cosmic neutrino background" exists.

The early universe was hot and dense and essentially acted as a large nuclear fusion reactor that produced helium. If one forms helium from protons, then positrons and neutrinos are a byproduct of the reaction. Modern theories of the early universe suggest that a large amount of neutrinos should have been present while this helium was being formed. The recently released WMAP data agrees with this theory, and with Earth-bound particle-collider experiments, suggests that the early universe did indeed have a large concentration of neutrinos.

Aside from neutrinos, what else was the universe made of? The answer to that was one of the key findings arising from the new WMAP experiment. A few years ago, NASA released information regarding the current make up and age of the universe. They found that the universe is approximately 13.73 billion years old, and currently consists of 4.6 percent ordinary baryonic matter (atoms), 23 percent dark matter, and the remaining 72 percent consists of the mysterious dark energy, and less than 1 percent neutrinos. However, this is in stark contrast to the early universe. New results show that when the universe was only 380,000 years old (13.7 billion years ago) it was composed of 12 percent baryonic matter, 63 percent dark matter, next to zero dark energy, 15 percent photons, and over 10 percent of was neutrinos.

Two other discoveries were made with this data; first, it was indirectly inferred that the first stars took more than half a billion years to form a cosmic "fog." The early stars created a interstellar cloud of electrons that scattered the microwaves. "We now have evidence that the creation of this fog was a drawn-out process, starting when the universe was about 400 million years old and lasting for half a billion years," said WMAP team member Joanna Dunkley of the University of Oxford in the U.K. and Princeton University in Princeton, N.J.

The final major discovery from the WMAP experiment is a set of tight constraints on what happened in the first trillionth of a second that the Universe existed. During this very early time, a period of rapid inflation occurred, which caused ripples in the fabric of spacetime to form. The newly described constraints allow cosmologists to eliminate many theories of what happened during this period, while it provides support for others. Principal investigator Charles Bennett of The Johns Hopkins University said that "it is astonishing that bold predictions of events in the first moments of the universe now can be confronted with solid measurements." I really couldn't agree with his sentiment more.

The results of the five-year study will be published in a series of seven papers that have been in Astrophysical Journal.

Matt Ford / Matt is a contributing writer at Ars Technica, focusing on physics, astronomy, chemistry, mathematics, and engineering. When he's not writing, he works on realtime models of large-scale engineering systems.